Not Applicable.
Not Applicable.
Not Applicable.
(5.1) Field of the Invention
The present invention relates generally to thermal ink-jet (xe2x80x9cTIJxe2x80x9d) technology and, more specifically, to a TIJ printhead structure and method of fabrication.
(5.2) Description of the Related Art
The art of ink-jet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, copiers, and facsimile machines employ ink-jet technology for producing hard copy. The basics of this technology are disclosed, for example, in various articles in the Hewlett-Packard Journal, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No.1 (February 1994) editions. Ink-jet devices are also described by W. J. Lloyd and H. T. Taub in Output Hardcopy [sic] Devices, chapter 13(Ed. R. C. Durbeck and S. Sherr, Academic Press, San Diego, 1988).
A simplistic schematic of a swath-scanning inkjet pen 100 is shown in FIG. 1 (PRIOR ART). The body of the pen 101 generally contains an ink accumulator and regulator mechanism 102. The internal ink accumulatorxe2x80x94or ink accumulation chamberxe2x80x94and associated regulator mechanism 102 are fluidically coupled 103 to an off-axis ink reservoir (not shown) in a known manner common to the state of the art. A printhead 104 element includes appropriate electrical connectors 105 (such as a tape automated bonding, xe2x80x9cflex tapexe2x80x9d) for transmitting signals to and from the printhead. The printhead has columns of individual nozzles 106 forming an addressable firing array 107. The typical state of the art scanning pen printhead 104 may have two or more columns with more than one-hundred nozzles per column. The nozzle array 107 is usually subdivided into discrete subsets, known as xe2x80x9cprimitives,xe2x80x9d which are dedicated to firing droplets of specific colorants on demand. In a thermal ink-jet pen, an ink drop generator mechanism includes a heater resistor subjacent each nozzle 106 with an ink chamber therebetween. Selectively passing current through a resistor superheats ink to a cavitation point such that an ink bubble""s expansion and collapse ejects a droplet from the associated nozzle 106.
Prior art for printhead structures and fabrication is typified by patents to Keefe et al., assigned to the common assignee herein. U.S. Pat. No. 5,278,584 shows an IMPROVED INK DELIVERY SYSTEM FOR AN INK-JET PRINTHEAD. U.S. Pat. No. 5,635,966, a continuation in part of the Keefe ""584 patent, shows an EDGE FEED INK DELIVERY THERMAL INKJET PRINTHEAD STRUCTURE AND METHOD OF FABRICATION.
The ever increasing complexity and miniaturization of TIJ nozzle arrays has led to the use of silicon wafer integrated circuit technology for the fabrication of printhead structures. For the purpose of the present invention, the xe2x80x9cfrontsidexe2x80x9d of a silicon wafer, or wafer printhead die region, is that side having drop generator elements; the xe2x80x9cbacksidexe2x80x9d of a silicon wafer, or wafer printhead die region, is that the opposite planar side, having ink feed channels (also referred to simply as xe2x80x9ctrenchesxe2x80x9d) fluidically coupled by ink feed holes through the silicon wafer to the drop generator elements.
In general, prior solutions to problems of working in silicon wafer technology to fabricate ink-jet printheads have taken two general forms. The first is to use a thin oxide membrane to define ink feed holes and provide a structural support for the associated resistor heaters. This technique has problems with the thin oxide breaking or distorting or both. A second solution relies upon an inherent slower etch rate of boron doped silicon in the etch processes used for defining a backside trench; the silicon under the resistor is heavily doped with boron to a depth of five to ten microns, masking the positions of the ink feed holes and leaving those feed hole regions undoped, thereby establishing different etch rate regions of the substrate. There appears to still be a lack of consistency in the etch rate of the boron-doped silicon; undercutting of the silicon at oxide interfaces occurs.
There is a need to provide an improved support structure under TIJ ink droplet firing resistors and to provide improved structural stability for TIJ ink feed channels.
In its basic aspect, the present invention provides an ink-jet printhead fabrication process using a silicon wafer, the process including: on a first surface of the wafer, forming an array of ink-jet drop generator location trenches interspersed with ink feed hole barrier trenches; filling said trenches with at least one material having a substantially equal or greater load bearing characteristic than silicon; and forming drop generator heater elements superjacent said inkjet drop generator location trenches and ink feed holes leading from a second surface of the wafer to said first surface between said ink-jet drop generator location trenches and adjacent barrier trenches.
In another aspect, the present invention provides a thermal ink-jet printhead device including: a silicon substrate having a first surface; a plurality of ink heaters; and a support subjacent each of said heaters embedded in said first surface, said support being a material having a load bearing characteristic equal to or greater than that of said silicon substrate.
In still another aspect, the present invention provides a thermal ink-jet pen, including: a body; an ink accumulation chamber within said body; and a printhead having a plurality of ink firing nozzles in a predetermined array, wherein each of said nozzles has an associated ink heater mounted on a silicon substrate printhead structure, each heater has at least one associated ink feed hole adjacent thereto and in fluidic communication with said ink accumulation chamber, and each said heater has a printhead structure support of a material having a substantially equal or greater load bearing characteristic than the silicon substrate load bearing characteristic, and each ink feed hole having inner sidewalls formed by said printhead structure support and outer sidewalls formed by an ink feed hole support formed of said material.
Some of the advantages of the process in accordance with the present invention are: it provides a three-dimensional control for forming ink feed holes and membrane dimensions measurable and verifiable early in the wafer fabrication process; it allows wider architectural design options to solve fluid dynamics problems associated with ink-jet printheads; it provides accurate wafer frontside alignment of ink feed channels and drop generator firing resistors; and it decreases technological demands with respect to architecture tolerances.
Some advantages of the employment of this process with respect to printheads fabricated therewith are: ink-jet printhead properties that define fluidics are set and verified early in the printhead fabrication process; a high firing frequency is attainable; increased nozzle-packing density is attainable; it provides for the incorporation of more intricate features such as particle filters; smaller nozzle sizes with concomitant ink drop volume reduction are attainable; and it provides wider design flexibility with respect to a ink viscosity.
The foregoing summary is not intended to be an inclusive list of all the aspects, objects, advantages, and features of the present invention nor should any limitation on the scope of the invention be implied therefrom. This Summary is provided in accordance with the mandate of 37 C.F.R. 1.73 and M.P.E.P. 608.01(d) merely to apprise the public, and more especially those interested in the particular art to which the invention relates, of the nature of the invention in order to be of assistance in aiding ready understanding of the patent in future searches. Objects, features and advantages of the present invention will become apparent upon consideration of the following explanation and the accompanying drawings, in which like reference designations represent like features throughout the drawings.